Ubuy.co.nz advertised a swing set this week at $5.70 for 78 weeks, or $444.60. A similar set at The Warehouse is $249.99. No one at Ubuy responded to a request for comment.

Financial adviser Lisa Dudson said consumers would choose the expensive options because they did not have the cash to buy them cheaper outright. Many people, she said, did not bother to work out how much something actually cost.

"They want it now and this makes it easy to have it now."

MyLayby.com is owned by the Chrisco Christmas hampers owners. Consumer chief executive Sue Chetwin said: "You are likely to be able to drive much better deals directly with retailers."

A MyLayby.com spokeswoman said it suited people who did not want to get into debt or could not get credit.

Mangere budgeting services boss Darryl Evans said two people had complained to his organisation that they were not able to cancel their MyLayby orders once they had paid them off, but the site's terms and conditions were clear about when and how you can cancel orders. He said he was hearing from a lot of young people who were taking out expensive personal loans.

"(MyLayby's) prices are comparable to retail stores. While you could get better deals with shopping around, it's definitely better than taking out a loan."

Lyn McMorran, of the Financial Services Federation, said the Credit Contracts and Consumer Finance Act had done away with rules that required disclosure of the lowest price of goods being lent against.

"(It) does allow for inflated prices and non-disclosure of how inflated they are ... you would have to wonder if such sites are using this as a bit of a loophole."